1.24 lakh deaths a year, one pollutant, one lever: what the SO2 study means
An IIT Delhi study puts a number on something Indian air-quality policy has argued about for two decades. The figure is large, the mechanism is unglamorous, and the intervention is largely settled.
By Nadia Rahman · Health & Science Reporter, Science
The short version
- A study from IIT Delhi estimates that curbing sulphur dioxide emissions from coal power plants could prevent more than 1.24 lakh deaths a year in India.
- SO2 is measured on the same network that produces the air quality index, but it does not drive the headline number the way fine particulate pollution does.
- Delhi's dashboard in early May showed ozone rising while nitrogen dioxide and carbon monoxide fell, an inversion that complicates the standard clean-air narrative.
Indian air-quality policy has spent fifteen years arguing about particles. That was a reasonable focus, because fine particulate matter has the clearest dose-response curve and the most legible public health case. But it left a second pollutant in an awkward position. Sulphur dioxide is measured continuously, it is regulated on paper, and the control technology for it has existed for far longer than the current debate.
That is the gap a study from IIT Delhi attempted to close in early May 2026. Its estimate is stark: curbing sulphur dioxide emissions from coal power plants could prevent more than 1.24 lakh deaths a year in India. That is not a projection of harm avoided in future. It is an accounting of harm currently occurring.
Why SO2 keeps getting lost
Two reasons. The first is that the index newspapers quote is dominated by particulate matter and ozone, so a city can improve its headline number while its sulphur dioxide load tells a different story. The second is that SO2 converts to sulphate aerosol close to its source, which makes it a regional problem rather than a purely local one. A plant hundreds of kilometres away can be part of what a city breathes.
Delhi's own readings in early May illustrated the problem in miniature. The city's air quality dashboard showed ozone rising while nitrogen dioxide and carbon monoxide declined, Indian Express reported on May 6. Ozone is not emitted at the tailpipe; it forms in sunlight from other pollutants. A shift in the mix is exactly the situation in which a single headline number stops being informative.
- The study's estimate: more than 1.24 lakh deaths a year attributable to sulphur dioxide emissions from coal power plants.
- The instrument: continuous SO2 monitoring on the national station network, which is what makes an attribution estimate possible at all.
- The control: emission limits applied at the source, which is an engineering problem rather than a behavioural one.
What the study does not do is say how quickly any of this changes. Sulphur limits in India have moved in steps, and plants need capital rather than announcements. The fair reading is that the number establishes the size of the prize, not the timeline for collecting it.
Sources — 3 references
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Nadia Rahman
Public health, clinical research and the long tail of epidemiology.
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